The terminology used in the description that follows is that standard for (and often unique as well to) sailing and yachting. A few sailing terms will be defined initially. Other sailing terms will be explained as they arise.                Hull—the entire floating structure of a sailboat.        Bottom—the portion of a sailboat that is immersed or partly immersed in the water and that provides the buoyancy supporting the entire sailboat.        Deck—a portion of a sailboat hull whose surface is generally horizontal, and on or in which the crew may stand, walk, or sit, and that is not part of the bottom.        Spar—a relatively rigid elongate pole that supports a sail in some way. Booms, masts, and sprits are types of spars.        Bow—the front portion of a boat hull.        Stern—the rear portion of a boat hull.        Line—a control rope on a sailboat. Sheets for controlling sail trim and halyards for raising sails are two types of lines.        Fore—towards the bow of a boat.        Aft—towards the stern of a boat.        Port—the left side of a boat.        Starboard—the right side of a boat.        Port tack—when the main boom of a sailboat is on the starboard side of a sailboat hull centerline.        Starboard tack—when the main boom of a sailboat is on the port side of a sailboat hull centerline.        Leeward side—the side of the boat on which the main boom is being carried at any given time.        Windward side—opposite of leeward side.        Beating, on a beat—sailing as close to the wind as is possible. (Sailboats typically have the ability to sail within 50 ° or less of the true wind. This ability is the reason that sailboats can sail a zigzag route to a point directly upwind from a starting point.)        
Hundreds of different sailboat designs exist, from hulls as small as 8 feet or less to well over 100 feet long. Most sailboats have V bows enabling them to slice through waves and chop efficiently. Such boats can be designed with relatively high freeboard (distance from the deck edge to the water) allowing the hull interior to remain relatively dry when higher waves are present. Other types have relatively low freeboard and typically are designed to rely on crew weight to oppose the wind force on sails.
Nearly every modern sailboat has a mainsail, the triangular sail extending behind the mast. The mast is a spar extending vertically from the deck. Sloop-rigged sailboats (sloops) also have a triangular jib sail also supported by the mast at the head, or topmost corner of the triangle. Some sloops have a bowsprit extending forward from the bow to which a jib is attached.
Many sailboats also are rigged to carry spinnakers, large sails used for running (sailing downwind) and reaching. Reaching refers to sailing at angles to the true wind between beating and running, or approximately from 50° to 160° from the true wind.
Spinnakers have typically had an isosceles triangle shape. A spinnaker is stowed when a sailboat is beating, and then lifted with a spinnaker halyard to place the head near the top of the mast when reaching and running. Spinnakers have one of the lower corners attached to a forward end of a spinnaker pole. Conventionally, the aft or rearmost end of the spinnaker pole has been attached to the front of the mast. When the spinnaker is stowed, the spinnaker pole is removed from the mast and stowed as well.
The invention pertains to spinnakers. A newer design of spinnaker pole is really not a spinnaker pole at all, but more accurately is termed a bowsprit. Such a bowsprit is permanently mounted in the bow of the sailboat. These usually can be retracted along an approximately horizontal path into the hull when the sailboat is not carrying the spinnaker so that the bowsprit will not be damaged by other sailboats crossing the bow.
A spinnaker carried on a retractable bowsprit is typically asymmetrical, i.e., the triangular sail shape is scalene rather than the generally isosceles shape of conventional spinnakers. The longest edge of an asymmetrical spinnaker is typically connected between the forward end of the bowsprit and the mast. The other vertical edge of an asymmetrical spinnaker is trimmed with a spinnaker sheet to a leeward point on the boat hull similar to that for a conventional spinnaker.
The advantage of an asymmetrical spinnaker is to allow faster reaching speeds than is possible with a symmetrical spinnaker. Some sailboats can sail more rapidly to a particular downwind point by reaching for a time, and then jibing to a reach on the opposite tack, rather than by running directly downwind. (“Jibing” refers to steering the sailboat stern through the wind from one tack to the other while sailing downwind.)
Since sailboats usually reach on downwind courses when asymmetrical spinnakers are hoisted, the paths of sailboats competing in a race tend to cross on downwind courses. Rules under which sailboat races are conducted impose obligations on sailboats to avoid contact (read: collisions) with other sailboats. These rules apply such that in every situation, as between any two sailboats whose courses are converging, one must alter course to prevent contact with the other.
A scow is a type of sailboat that has a flat bottom, a relatively shallow hull, and a rounded, blunt bow rather than a V hull. Scows are usually sailed with significant heel. This lengthens the immersed water line substantially, increasing the speed potential of the sailboat. At the same time, the broad, flat bottom provides excellent stability when the sailboat is moored. Scows rely on crew weight to oppose the wind force tending to tip the boat. Asymmetrical spinnakers are now class legal on the largest scow now sailing, the 38 ft. A scow.
In the current A scow design, the bowsprit extends linearly through a fixed internal brace member and a deck fitting near the front of the deck. Because of the relatively shallow scow hull, the tip of the extended bowsprit is only a little above the deck level and close to the water.
For these reasons, asymmetrical spinnakers flown by scows tend to sweep the front deck, interfering with vision behind the spinnakers. The heeling of a scow only increases the vision problem. This leads to risky situations, with the crew's view of sailboats on converging courses obscured. In fact, the problem to some extent affects sailboats other than scows when flying asymmetrical spinnakers. This problem does not normally exist with symmetrical spinnakers since the mast-mounted spinnaker poles used with them supports the foot of the spinnaker a good distance above the deck.
One possible solution to this vision problem is to place a clear, flexible plastic window in the foot of the spinnaker. Unfortunately, it is not easy to put windows in spinnakers. Spinnakers are made of relatively light material. The clear plastic material from which windows are made is substantially heavier and stiffer that spinnaker material, leading to poor spinnaker shape and slower sailing.
Accordingly, another solution to the problem of poor visibility with asymmetrical spinnakers is necessary.